Some heating circuits not working well - what to do..?

[reb78]

Our house central heating seems to have a real mish mash of microbore in places and 15 and 22mm pipework in others. Most of it works ok to be honest so we have left it alone, but our extension has a set of five rads that work poorly. To try to fix this, we fitted a JG Speedfit underfloor heating manifold with a separate pump to the rest of the system. The flow branches into two before the pumps and one of these , eeds the pump to the manifold. The return from the manifold feeds into the system return. Each rad as its own flow and return to the manifold. Two rads have good flow - these have runs of about 3m and 5m of 10mm pipe to and from the rads. Of the other three, they are 7.5m, 12m and 14m runs of pipe from the manifold. Curiously, the 12m distant rad heats up fairly well. The 7.5m one is ok but not great, and the 14m one rarely gets very hot. If I close the returns on four, whichever is left open heats up nicely so I know the pipework is all clear (we flushed it, and the rads when we fitted the manifold anyway).

Any ideas on this?

The pipework was hard to bleed initially but we pressure bled it as per - https://www.mig-welding.co.uk/forum/threads/heating-manifold-one-circuit-not-working.136945/

I also took the advice off of that thread and removed the flow valves from the three troublesome circuits. I left them in place for the two that were working but cant imagine thats causing a restriction.

I dont really want to raise the floors to replace the pipework at this point although ultimately that may be what we end up doing. As above though I know the pipes and valves are clear and should run.

The pump is a new Grundfos UPS3 15-50/65 150. Even set on its highest flow rate, water doesnt circulate through these five rads well. Is there a more suitable pump for microbore and manifolds we should have used? The pump on the rest of the house is the same type and that flows just fine and serves 12 rads via a much more convoluted system.

 

[dave h 2]

If you didn't put enough inhibitor in the gas produced may have re-instated the original airlock.
It may be the other pump is robbing the new one due to the less restrictive older pipework. The stronger one may even be back pressuring the return depending on where the two returns meet. try turning the old one down and/or restricting the old rads more.

 

[gaz1]

a note here those pipes dont look to be minibore but look like 15mm plastic

force flow your rads to do this shut down your other rads close the return side down on all rads but the once you need on ( except 2 rads ) and force the water through the pipes to the radiators causing you issues by opening both sides of the rad valve to full flow make sure you turn them on and off a couple of times as this knocks off any crud that might be on the valves so full flow can be done

run it for 10 mins each rad while turned on as this will remove any trapped air within those pipes remember it dosnt always do it

Its a vented system Gaz due to the Rayburn in the system. This might be part of the problem as the pressure is only what the header tank provides.

a vented system shouldnt have much trouble when a pump is fitted though as long as you have a good header tank it shouldnt suck air into the pipes when first starting of the pump

i still think you have crud sediment in the pipes / air issues

force flow each rad until red hot to touch 10 mins is normally enough time for this and should flow out any air thats trapped in the pipes in both flow and return

the 1 rad left on need to be the furthest from the pump whilst trying to flow the heat through the issue rad/rads as your playing with a wood burner which needs flow

when all the rads are red hot close that last one down on the return flow and then a 1/4 turn to open the valve open the return pipe on the other rads the same way check the flow of heat through those pipes to the rads and shut down the rad which you had left on that is the farthest away

the rads should equal the same temp per rad thats turned on

 

[reb78]

If you didn't put enough inhibitor in the gas produced may have re-instated the original airlock.
It may be the other pump is robbing the new one due to the less restrictive older pipework. The stronger one may even be back pressuring the return depending on where the two returns meet. try turning the old one down and/or restricting the old rads more.

I dont think its an airlock as I can get flow to each of the five rads if I turn the other four off

 

[gaz1]

a warning have a low fire in the rayburn at the time when doing this

you want enough heat to travel to the rads when testing them but not too much heat if that system has issues

 

[reb78]

a note here those pipes dont look to be minibore but look like 15mm plastic

force flow your rads to do this shut down your other rads close the return side down on all rads but the once you need on ( except 2 rads ) and force the water through the pipes to the radiators causing you issues by opening both sides of the rad valve to full flow make sure you turn them on and off a couple of times as this knocks off any crud that might be on the valves so full flow can be done

run it for 10 mins each rad while turned on as this will remove any trapped air within those pipes remember it dosnt always do it

Its a vented system Gaz due to the Rayburn in the system. This might be part of the problem as the pressure is only what the header tank provides.

a vented system shouldnt have much trouble when a pump is fitted though as long as you have a good header tank it shouldnt suck air into the pipes when first starting of the pump

i still think you have crud sediment in the pipes / air issues

force flow each rad until red hot to touch 10 mins is normally enough time for this and should flow out any air thats trapped in the pipes in both flow and return

the 1 rad left on need to be the furthest from the pump whilst trying to flow the heat through the issue rad/rads as your playing with a wood burner which needs flow

when all the rads are red hot close that last one down on the return flow and then a 1/4 turn to open the valve open the return pipe on the other rads the same way check the flow of heat through those pipes to the rads

the rads should equal the same temp per rad thats turned on

The pipes you can see on the other thread are 15mm as you say but they join to the 10mm stuff under the floor so they are just a short run to get from the manifolds to the pipework under the floor boards.

I dont think it can be crud Gaz - I have flushed it all multiple times (easy to do with the manifold isolated as i can just connect a hose)

I have done the rest of what you suggest already as it seemed logical to try that but the furthest rad is rubbish, just no heat to it at all.

 

[reb78]

a warning have a low fire in the rayburn at the time when doing this

you want enough heat to travel to the rads when testing them but not too much heat if that system has issues

Central heating only kicks in when the stat half way down the thermal store reaches 55C so its somewhat disconnected from the rayburn (at least not directly connected). The top of the store will get hot and stay at that temp for hot water.

 

[gaz1]

flush it all you want crud can still be within the system only way to get it out is remove the pipes clean them and refit or just refit new pipes in

but did you do what i said with just those 4 rads on only as rest of the house is shut down as thats what im wanting you to do this time as no other rads are on only those 4 giving issues

 

[reb78]

flush it all you want crud can still be within the system only way to get it out is remove the pipes clean them and refit or just refit new pipes in

but did you do what i said with just those 4 rads on only as rest of the house is shut down as thats what im wanting you to do this time as no other rads are on only those 4 giving issues

No, as I misunderstood what you meant. On the manifold, I can turn off four rads and will get good heat to the fifth is what i meant (the rest of the house is running off of the other pump). So doesnt this show the pipes are clear with no air?

 

[gaz1]

no air can still be within any system when you fill it back up and it takes a while to get rid of all of it

thats why you need to bleed a rad every now and again to get rid of the cold spot in a rad as its collected the air within it

im 2 weeks after removing the pump fitting a new capicitor within it and refitiing the pump again and theres still air within the pipes

 

[gaz1]

a query here have you got 2 pumps running at the same time run from the same feed into 2 different systems ?

have you checked your pump for spinning

 

[reb78]

a query here have you got 2 pumps running at the same time run from the same feed into 2 different systems ?

have you checked your pump for spinning

Yes - both pumps come on together. I did wonder if one robs the other of flow as above but not sure how I would get them to come on separately. At the moment, the main house (12 rads) pump is on minimal flow and the manifold pump is on max - so something isn't right

They both appear to spin. They are new grundfos ones that throw errors if they arent turning and flash a red light at you. The one on the manifold certainly seems to be circulating as its getting the rads that work hot.

 

[gaz1]

the pumps can be mismatched so one robs from the others flow ( spins faster )

also depends on what size of pipe that you have before its split into 2 systems 28mm-32mm size of pipe thats split into 22mm

another note is that one side can flow and return much faster due to the use of 2 pumps the only way to stop this is to allow more flow through the other circuit whilst reducing the others flow ( its similar to the water hot tank returning to the boiler faster ) or switch to a single pump system

if you have the pump switches for speed turn one to number 2 whilst the other is turned to 3 ( pump speed 1 or 2 or 2-3 for faster flow of water )

alternate way is to try by unpluging one plug from the house circuit and just allowing the other pump to the minibore system to run that system can be timed if needed so you get 15 mins to either system timed whilst the rayburn is at full heat

 

[DanZac]

Probably a stupid question, and I haven't gone back to your other thread but have you worked through the system trying to "balance" it?

The Simple Guide to Balancing Radiators | UK Radiators

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ukradiators.com

 

[Mikes]

Post up a simple sketch of how the two pumps are connected to the heat store please so we can get the full picture of the system.

 

[gaz1]

Our house central heating seems to have a real mish mash of microbore in places and 15 and 22mm pipework in others. Most of it works ok to be honest so we have left it alone, but our extension has a set of five rads that work poorly. To try to fix this, we fitted a JG Speedfit underfloor heating manifold with a separate pump to the rest of the system. The flow branches into two before the pumps and one of these , eeds the pump to the manifold. The return from the manifold feeds into the system return.

before you fit the new pump to the manifold how did your system work before

note minibore pipe means faster flow of water through to the rad

what sort of issues did you have

 

[gaz1]

Probably a stupid question, and I haven't gone back to your other thread but have you worked through the system trying to "balance" it?

The Simple Guide to Balancing Radiators | UK Radiators

When it comes to balancing radiators you might not know where to start. Luckily, our simple guide to balancing radiators has all of the info.

ukradiators.com

balance wont work as theres 2 systems at play from one feed pipe

it would take balancing both systems out correctly whilst playing with pump speed and also the flow and return of water back to the boiler

 

[reb78]

 

[reb78]

You can see the central heating flow from the thermal store above. This is 22mm pipe. The return is the very bottom inlet. This also shows pipework to the two pumps - the manifold pump is clear to see. They are both triggered when the thermostat behind the 'Tee' to separate the flows gets to 55C. I am wondering if this Tee should have been so that the leg of the T takes flow from the tank and the top branches of the T go off to each pump.

Pumps were set on 3 (manifold pump) and 2 (main house pump). I have reduced the main house pump to 1 to see if it changes anything.

One part of the problem is that its designed to come on and send flow round when that point in the tank gets to 55C. Often this doesnt seem to mean the pump is on for long if the Rayburn isnt churning out the heat, so if the manifolded section has poor flow, this may contribute to there being little time for that system to heat up.

 

[addjunkie]

Probably a stupid question, and I haven't gone back to your other thread but have you worked through the system trying to "balance" it?

The Simple Guide to Balancing Radiators | UK Radiators

When it comes to balancing radiators you might not know where to start. Luckily, our simple guide to balancing radiators has all of the info.

ukradiators.com

Did your replace the flow valves with plugs as suggested in the other thread. I suspect with the low flow rates you are getting preferential flow as water will take the easiest route. If all circuits work individually you will need to balance as suggested.

Disconnect the other pump, and see if things improve. Are the returns into the same place?